Known engine management systems (EMS) monitor and control the running of an engine in order to meet certain pre-set or design criteria. Typically these are good driveability coupled with high fuel efficiency and low emissions. One such known system is shown schematically in FIG. 1. An internal combustion engine 10 is controlled by an engine control unit 12 which receives sensor signals from a sensor group designated generally 14 and issues control signals to an actuator group designated generally 16. The engine control unit 12 also receives external inputs from external input block 18 as discussed in more detail below.
Based on the engine performance data derived from the sensor input from the sensor block 14 and any external input from the external input block 18 the engine control unit (ECU) optimises engine performance by varying the relevant performance input variable within the specified criteria.
Typically the sensor block 14 may include sensors including mass air flow sensors, inlet temperature sensors, knock detection sensors, cam sensor, air/fuel ratio (AFR) or lambda (λ) sensors, and engine speed sensors. The external input block 18 typically includes throttle or accelerator sensors, ambient pressure sensors and engine coolant temperature sensors. In a spark-ignition engine the actuator block 16 typically comprises a fuel injector control and spark plug operation control. In a compression ignition engine the actuator block typically comprises a fuel injector.
As a result, for example in spark ignition engines, under variable load conditions induced by the throttle under driver control, the sensors and actuators enable effective control of the amount of fuel entering the combustion chamber in order to achieve stoichiometric AFR, and of the timing of combustion itself.
Known engine management systems suffer from various problems. EMS technology remains restricted to parameter based systems. These systems incorporate various look-up tables which provide output values based on control parameters such as set-points, boundaries, control gains, and dynamic compensation factors, over a range of ambient and engine operating conditions. For example in spark ignition engines spark timing is conventionally mapped against engine speed and engine load and requires compensation for cold starting. In compression ignition engines fuel injection timing is mapped in a similar manner. As well as introducing a high data storage demand, therefore, known systems require significant initial calibration. This calibration is typically carried out on a test bed where an engine is driven through the full range of conditions mapped into the look-up tables. As a result the systems do not compensate for factors such as variations between engine builds let alone individual cylinders, and in-service wear. Accordingly the look-up tables may be inaccurate ab initio for an individual engine, and will become less accurate still with time.
In one aspect known systems control vehicle performance based on a consideration of engine conditions together with mappings. These mappings are derived during vehicle calibration and can include physical parameters related to engine geometry. Generally much of the engine performance data is very indirect and is based on multiple inferences from sensors together with the mapped or modelled data which can give rise to inaccuracies arising from the inferences made or from differences between vehicles based on production tolerances or indeed differences between conditions in individual cylinders within an engine. The latter is mainly due to differences in air and inert gas paths, temperatures of the cylinder walls and production tolerances of valvetrain and piston/crankshaft geometry. Furthermore such approaches do not compensate for changes in performance arising from in-service wear.
One known system comprises adjusting performance input variables to the engine to control engine torque to a target. A problem with this is that the engine torque is in fact inferred from easily measurable variables such that airflow in a gasoline engine or fuel flow in a diesel engine. Accordingly the value for torque that is derived is indirect and inaccurate, suffering from the disadvantages set out above. Although torque sensors are known, these are costly and are not robust. Known systems also derive a measure of engine frictional losses represented by the friction mean effective pressure (FMEP). However in known systems these values are currently mapped or modelled at the engine manufacture stage and hence suffer from the problems set out above.
The invention is set out in the claims.